In the past, an electromagnetic agitator that generates a shifting field by making low-frequency current or high-frequency current flow in an electromagnetic coil in order to agitate a molten metal, a mechanical agitator that directly agitates the molten metal by a rotary impeller inserted into the molten metal, or the like has been used to agitate the molten non-ferrous metal or other metal. The main objects of all these devices are to uniformize the composition of the molten metal present in a furnace, to uniformize the temperature distribution of the molten metal, to reduce the time for melting in a melting furnace, and the like.
However, the device using the electromagnetic coil required large power consumption or complex maintenance and had a problem in that initial costs are high. Further, in the case of the mechanical agitator, there have been many problems in that the abrasion of the rotary blades is apt to occur, the costs for the replacement of the rotary impeller are very high per year, the stop of the furnace for a long time during the replacement cannot be avoided, and loss caused by down time is considerable, and the like. Further, a permanent magnet-rotation shifting field system also has started to be used in recent years. However, there also is a problem in that performance is limited due to the heat generated from a furnace reinforcing plate, which is made of stainless steel.